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A Guide to Modern Mortar Systems

By FinnishInfantryOfficer

This guest article is by a serving Finnish Army Officer, who prefers to remain anonymous. He is an authority on artillery and infantry weapon systems, as well as an active contributor to discussions on key defence topics.

Mortars have been used for centuries, primarily as siege weapons. They differ from conventional artillery by firing projectiles at higher angles, at lower velocities, over shorter distances. Mortars as we know them today first saw light of day during WW1, when the British Army fielded the Stokes 3.2” (81mm) trench mortar. This had a smoothbore tube attached to a circular metal baseplate that was dug-in to the ground to absorb recoil. It had a range of 700 metres and could fire around 25 bombs per minute. Its stand-out feature was that it was truly man-portable.

Above: Stokes 3″ mortar. The first modern mortar from 1915.

After the war and especially during the 1930s, mortars in multiple calibres were honed into the shape and form they exhibit today. Mortar sights from the 1930s remain common and work seamlessly with mortar from 1990s. Advances in metallurgy and manufacturing combined with modern fire control systems that calculate range precisely, have improved effectiveness, reliability and robustness, but the fundamental design and operating concept remains unchanged.

During World War 2, 3″ mortars (81 mm) were used widely. Since then, the 120 mm mortar has become a common standard across NATO. Indeed, the only major Western army not to use this calibre of mortar is the British Army.

02 – Review of current systems

The British Army still uses a modern version of the original 3” mortar developed by Stokes during WW1. The L16 81 mm mortar has been used since the mid-1960s. It is fully man-portable with the components divided into loads that can easily be carried dismounted. It has proved to be an extremely reliable system that delivers excellent effect. It has been mounted in the FV432 APC to provide a mobile firepower for infantry battalions.

UK 81 mm mortar

The British Army later adopted a light 2” mortar for use at platoon level. This fired smoke and HE, but was of limited use due to its lack of accuracy. It was later replaced by a 51mm mortar with improved sights and ammunition.

More recently, the 60 mm Hirtenbirger mortar has seen UK service, but since it provides only marginally increased firepower over a 51mm mortar while weighing almost as much as an 81mm mortar, its utility is questionable.

The US, German, French, Italian and many other NATO armies have standardised around a heavy mortar of 120 mm. Primarily used in a towed application, 120 mm mortars are the most ubiquitous of heavy mortar systems in service today, thanks to their ease of use, low cost and low crew requirements. Such weapons have seen worldwide service over the last 50 years. You’ll even find insurgents making such mortars and ammunition in garages in Aleppo.

MO 120 mm towed mortar of the French Army

Typical range for a 120 mm towed smoothbore mortar is around 7.8 km using a 2 m barrel. Costs are typically around €370,000 per system. A 120mm mortar with towing kit weighs around 500kg. This is light enough to be hauled across short distances, but too heavy and bulky to be man-portable beyond a few hundred metres. The crew usually consists of 5-7 soldiers. Heavy mortars are usually operated either by infantry or artillery units and deployed according to the standard operating practices of each arm. More often than not, mortars will be owned by infantry units and as such are considered to be a battalion commander’s own “pocket artillery” with approximately 4 to 12 tubes issued per infantry battalion.

Self-propelled mortars existed during WW2, but were generally light weapons. Later, the Soviet 2S9 and a number of other successful post-war medium mortar designs saw service. The US Army mounted a standard 120mm mortar system in its M113 APC, which has now been transferred to its Stryker 8×8 infantry carrier vehicle. The Soviet Army developed the 2S4 Tyulpan 240mm self-propelled super heavy mortar. While offering supreme firepower, it has a slow rate of fire.

The US Army’s m1129 Stryker 120 mm mortar vehicle. This is a highly effective, highly mobile system. Although it lacks the precision and speed of engagement that turret-mounted systems offer, it is less expensive.

In the late 1990s. Finland and Sweden formed a partnership to design and produce a self-propelled mortar. The result was the AMOS 120mm system. This is a breech-loaded, double-barrel design with two 3 metre tubes. It has a 10km range, a Multiple Round Simultaneous Impact (MRSI) capability and a fully-automated fire control system. All of these attributes were unheard of before.

Swedish Army 120 mm AMOS system mounted on a CV90 platform.

When Sweden dropped out of the programme, Finland was left to finalise development, but fortunately Sweden then adopted it. With the eventual price reaching an eye-watering €5 million per system, the AMOS system begs the question whether the money it cost to develop could have been better spent on some other artillery system? Original plans called for 24 systems in six mortar companies, each with 4x AMOS systems, but the final outcome was 18 in total with three per mortar company. The AMOS design led to its single-barrel brother, NEMO, which builds on the same system advantages making them the world’s most capable self-propelled mortar systems, at least for those with deep enough pockets.

Light artillery: worst enemy or best friend

03 – Comparison with other indirect fire weapons

As stated earlier, heavy mortars belong to either infantry or artillery units and this in turn dictates their relationship to other indirect fire weapons. They generally pack a bigger punch over a shorter distance. The obvious pecking order established by most countries that use such weapons is as follows:
– 60mm / 81mm mortars are used at company level
– 120mm mortars are used at battalion level
– 155mm howitzers are used at brigade level.

Declining numbers of soldiers in armies across the globe has seen the need to do more with less and often the solution has been mixed battalion battle groups. The basic premise is to take an infantry battalion and to add whatever supporting units are needed to execute a mission. This has brought tube artillery down to battalion level and, in some cases, stimulated a discussion about what the appropriate level of fire support for battalion-size battle group should be. If we strip the battalion of indirect fire weapons and add weapons that a brigade might have at its disposal, we’re left with following options with their pros and cons:
– 60mm mortar – low logistical footprint and truly man-portable, but short range (~3,800 metres) and limited effect, with minimum penetration of fortifications or buildings
– 81/ 82mm mortars – man-portable, efficient, with the highest ratio of number of kills per tonne of ammunition carried, but short-range (~5,600 metres) and limited effect
– 120mm mortar – very good effect: near misses can destroy lightly armoured vehicles, but only modest range increase over 81mm (~10,000 metres) and less portable
– 105mm howitzer – good range (~17,000 metres) and very good effect on par with 120mm mortar, but requires greater logical support, more crew training and is more difficult to transport
– 155mm howitzer – outstanding range and effect, but requires considerable logistical support including dedicated wheeled vehicles or self-propelled tracked platform.
Picture 1. Despite the apparent simplicity of the 120mm heavy mortar, it still needs a large amount of ancillary equipment, ammunition and has a crew requirement beyond what an RG-32 can carry.

Despite the apparent simplicity of the 120mm heavy mortar, it still needs a large amount of ancillary equipment to support it, plus ammunition and a crew requirement beyond what vehicles like the RG-32 can carry.

Ultimately, the mission will dictate the ideal combination of weapons needed. It must also be said that a 120mm mortar is not necessarily a substitute for 105mm howitzers. Finland has adopted both a 120mm mortar and a 122mm howitzer in their new battlegroup structure. Together, they are a good example of what massed fires mean. A single battle group has an impressive 42 indirect fire weapons and is capable of firing 468 rounds per minute, if all weapons are aimed at a single target.

Like all towed weapons, heavy mortars suffer from inability to “shoot and scoot.” Of course, trained crews can mount and dismount their mortars quickly enough to qualify as mobile units under optimal conditions, but invariably real combat will introduce other factors that delay the un-packing and re-packing of equipment. Mounted heavy mortars, such as Cardom, have a quasi “shoot and scoot” capability through TALIN or other systems that feed fire control systems the mortars location, deflection and elevation at any given moment. More importantly, they allow the tubes to be dispersed making mortar units less susceptible to counter mortar fire. The downside as always is the price; towed weapon systems cost close to €1 million each, while wheeled platforms cost many millions and defeat any concept of simple and cheap artillery that mortars are supposed to offer.

The UK continues to use the L118 105 mm Light Gun. Compared to towed 120 mm mortar systems, this has double the range: 16-17 km. It has proved to be extremely useful and has seen considerable service across all British Army deployments over the last 30-40 years. it is now starting to show its age. As the UK considers the need to replace or least supplement the L118 105 mm gun, a towed 120 mm mortar could provide a worthwhile increase in capability at an attractive cost.

Finnish Army NEMO – A highly capable 120 mm mortar system. Its ability place five rounds simultaneously on a target is unequalled by any other mortar system.

From a technical viewpoint AMOS and NEMO have caught up with 105mm howitzers. While having shorter range they can outgun any 105 with their MRSI and rate of fire. Also, they are inherently capable of “shoot and scoot” fire and movement, which cannot be said of towed artillery. Shorter range means being closer to the enemy, but also allows fire missions to commence with fire for effect, because external influences are fewer and computerised fire control ensures firing values will be accurate, leading to faster engagement times. Hitting a target with the first few rounds is much easier and more certain from 5km than from 13km. Also inherently smaller round dispersion, coupled with faster rates of fire favour the mortar when supporting troops in contact. It should be noted that even battalion battle groups should be able to conduct fire missions that reach an enemy’s rear area, even at ranges of 15 km behind the FEBA. Perhaps an ideal fire support composition for battalion battle group would be fire support battalion comprised of two batteries of 105mm plus a company of 120mm mortars. South Africans have very successfully mixed tube artillery, rocket artillery and heavy mortars into same organisation and there is much to learn from their methods.

120mm mortars do not necessarily replace light towed artillery. This is a Canadian 105mm C3 howitzer.

04 – Conclusion

Towed 120mm heavy mortars will remain a primary source of firepower at battalion level for many years to come. Modern self-propelled mortar systems comprise about 1-2% of all heavy mortars used today and using them to replace the remaining 98% would require immense investment. Until then, armies will have to make do with what they have got and manage obsolescence by developing new tactics, adding subtle refinements, such as mortar mounted TALIN and other FCS systems. Irrespectivective of any enhancements, it still takes a painfully long time to dig a pit for a mortar base plate in frozen ground. However, mounted systems come at a cost and depleted forces with fewer numbers means a reduced ability to “make it rain.” A mortar company of 12 mortars can fire 144 rounds per minute, whereas a company of three AMOS vehicles can fire 36 rounds per minute. Choosing between towed and self-propelled systems is more subtle than just comparing a rate of fire of 144 versus 36 rounds per minute. A 120mm mortar system mounted in an 8×8 platform may be an ideal compromise, but may lack precision. Costs are between those of a towed system and NEMO.

Ultimately, this article is nothing more than a rough guide to current mortar systems; and it doesn’t exist to promote AMOS above other mobile systems. The objective is to highlight the trade-offs that need to be made between choosing a larger quantity of older, but capable and lethal legacy systems versus a smaller number of modern, efficient systems in any economically constrained environment. As is often said: quantity has a quality of its own.

De facto inability of fin-stabilised mortar bombs to make use of RAP (wind issues) wasn’t mentioned (but to be honest, I never blogged on that either).

The importance of illumination should be mentioned. The new IR ILLUM rounds help only those with NVGs and other near-IR night sights by illuminating the battlefield in a way that’s not visible to the naked eye. This is fairly new and not yet icnorporated into most Western land forces AFAIK.
It’s clealry no Schwerpunkt activity, so there’s a strong case for making it the job of organic (platoon to battalion) indirect fires. It might even be the best justification for platoon-level commando mortars.

Prices offered for towed mortars (per piece and with vehicle) differ so much that certain assumptions should be clarified (I suppose a hardened 4×4 vehicle was assumed).

Troubles with recoil from 120 mm mortars on wheeled (and alson tracked) platforms have been neglected (some vehicles can be shaken apart by the recoil, and mitigating it means to add a recoil mechanism akin to what a 105 mm hwoitzer has).

105 mm SPGs and tanks with high maximum elevation 105 mm gun turrets that can double as SPGs were neglected. 105 mm SPGs were quite a thing in the past before NATO stnadardised on 155 mm (possibly with ICM/DPICM in mind) – remember the Abbot.

“Towed 120mm heavy mortars will remain a primary source of firepower at battalion level for many years to come.”
Or maybe they’ll be massacred by counterfires in the next major war between modern armies and become considered as obsolete as blue uniforms and battle cavalry by ’15.

Arty would often be out of range and is usually SP and shoot & scoot capable now. Effective counterfires against SPGs or even MRLs require so much sophistication that their process would likely not be reliable enough to justify the effort.

I suppose bipod mortars would get hammered because they lack shoot & scoot (for mediums there wouldn’t be much ground to use within range anyway) and thus CAN be hit. Anything less mobile than those 120 mm portée mortars that can be lowered and raised on the rear of a pickup should better be a commando mortar. Their small projectiles with very low apogee are less susceptible to radars.

Let me ask you one thing. How far away from lead battalion do Russians put their artillery battalion or same with Germany or USA? What is the planned range from furthermost maneuver element when they come into contact? 5, 10, 15, 35km?

I’ve never seen any written preferred distance, but 18-22 km distance to target is well-liked because it’s possible with good dispersion, standard HE (no BB or RAP) with some coice of elevations (MRSI possible) and standard SMK works as well (I doubt there’s any BB or RAP for SMK available at all / there are few mortars in the Heer).

I highly doubt anyone in the German field manual writing teams would dare to suggest that trying to keep a certain distance to the most forward battalion would make much sense.

Do you have any experience with AMOS or NEMO in direct fire mode? Specifically, how does accuracy compare to tank guns or tube artillery in direct fire mode? I would expect tanks to win out at longer ranges.

If MBTs eventually go to the larger, heavier 130mm gun, they’ll have room for even fewer HE/HEAT/MPAT multi-purpose rounds. A gun-mortar on IFVs could supplement them.

A mortar turret has greater elevation , as well as a shorter barrel than MBTs. Both are useful qualities in urban environments

Imagine an IFV company providing supporting mortar fire for another company in the battalion. 14 NEMO-level tubes could rain down a lot of mortar bombs in a short period of time. Maybe not as good as dedicated mortar vehicles, but quantity has a quality of its own.

Obviously training gunners in indirect as well as direct fire missions would be an issue. But perhaps a lot of the indirect side could be automated.

France, South Africa and Israel use breech loaded 60mm mortar on number of AFV. I think 81mm would be good size for such weapon to accommodate large enough HEAT/MP warhead in direct fire role. I can think of quite a few reasons why dual role in this situation would be bad and having dedicated indirect support unit is better but I think breech loaded mortar for close in direct support and ability to shoot smoke and illumination indirectly would be very beneficial.

Also, 81mm might be too small to create breach holes in rebar-reinforced concrete. It’s unclear if a 120mm mortar HE round would be good at this either, but at least it’s bigger.

What are some reasons why dual role wouldn’t be a good idea?

I could see having both. Have dedicated 120mm mortars as primary indirect fire assets, but also 120mm Gun-Launcher-Mortars (GLMs) on IFVs to provide supplementary indirect fires, direct support to infantry, and long range, anti-tank missile fire.

Of course if we could have both that would be good. The problems I see are C2, logistics, availability and planning the units use.

120mm rounds are pretty bulky, also the barrel and breech would take a lot of space so will there be space left for infantry or other weapons ammo? Would the vehicle be dedicated for fire support? I’m not convinced about the need to launch missiles from this thing. Firing position requirement differ greatly for missiles and mortar. I would prefer something with either 20mm or gatling .50cal with and 81mm breech loaded, two per MIV/Stryker/equivalent company. In permissible environment they can use all weapons to support infantry and against peer enemy they could park close by behind cover and lob IR smoke to cover infantry advance.

The Nemo turret is almost comically small for the size of the gun, so I can’t imagine the breech takes up that much space. For the GLM implementation, I would redesign it to store ammunition in a bustle rack rather than the hull. A two-man turret with a 30mm and 120mm together would certainly be larger than just a 30mm turret alone. But how much more it would intrude into the passenger area is unclear.

120mm mortar bombs are much smaller than TOWs, which are carried in the troop compartment of Bradleys, and are manually loaded by dismounts from the rear compartment. Not ideal.

Maybe you lose one dismount, or increase the size of the vehicle, but you gain a very flexible weapon. Trade-offs.

Obviously no such system exists, so the $$ needed to build it would likely put it out of reach. And it seems like the US Army would prefer a simpler solution. They don’t even seem to care much about going from 25mm to 30mm, and were willing to dump the ATGM launcher on the GMV.

If MBTs stay with 120mm guns for the time being, perhaps the need to have a supplementary direct-fire HE tosser is lower. But if we move to 130mm, and go from ~40 rounds stowed to ~30-35, tanks will have a harder time carrying a useful mix of sabot and MP.

“Ultimately, this article is nothing more than a rough guide to current mortar systems; and it doesn’t exist to promote AMOS above other mobile systems.”

“The AMOS design led to its single-barrel brother, NEMO, which builds on the same system advantages making them the world’s most capable self-propelled mortar systems”.

Unfortunately, these 2 statements seem to contradict each other since the author, despite being a professional in the field of mortars, mysteriously forgot to mention the RAK system, being easily just as good as AMOS/NEMO are.

Even though the English sources are scarce about this system and/or contain errors: the above link is the best what I could find in English, but here is the link to the Polish source describing RAK’s correct rate of fire: 7-10 rounds/minute (the same as NEMO’s).

Interesting that UK MOD is announcing the end of the 60mm mortar as a platoon weapon (along with the withdrawal of the LSW and LMG). If they are replacing it for something more effective, or as effective but with other advantages (lighter) then great, but I hope it’s not a loss of firepower overall.